a person who has killed somebody deliberately and illegally synonym killer a convicted murderer a mass murderer (= who has killed a lot of people) See related entries: CriminalsExtra examples Does the death penalty deter would-be murderers? He protested his innocence and promised to help police track down the real murderer. The identity of her murderer has not yet been revealed. The murderer has struck again. A convicted murderer was on the run last night. How do we know he’s not a mass murderer?